Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond annotations (readOnlyHint, idempotentHint, destructiveHint false), the description discloses that the calculation is approximate, may differ due to fuel cost adjustments and discount conditions, and that the service participates in an affiliate program. This adds valuable context about result reliability and potential bias.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is efficiently structured: the first sentence states purpose, the second gives usage guidance, and the disclaimer is concise and necessary. It front-loads the core function and contains no redundant information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a tool with 9 parameters and no output schema, the description explains the main workflow and caveats. It could mention the output structure more explicitly, but the read-only annotation and clear purpose make it sufficiently complete. The auto-selection of plan_ids when omitted is covered in the schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

With schema description coverage at 89%, the schema already documents most parameters. The description adds the key semantic relationship: monthly_kwh and current_monthly_bill_yen are alternative inputs, and plan_ids originates from search_plans. This clarifies selection logic not present in the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's function: calculating the annual cost of each plan and the difference from the current contract, using either monthly kWh or back-calculation from the monthly bill. It uses a specific verb '試算する' and resource, distinguishing it from sibling tools like compare_plans and search_plans.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear parameter guidance (use monthly_kwh if usage is known, current_monthly_bill_yen otherwise), but it does not explicitly say when to use this tool versus alternatives like compare_plans or get_switch_link. Usage context is implied rather than contrasted with siblings.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.